1. Field of the Invention
The present invention relates to devices, systems and methods for sensing temperature. More particularly, the present invention relates to sensing temperature of a drag cup within the motor of a rheometer.
2. Background of the Invention
Rotary rheometers, viscometers or viscosimeters are typically used to measure fluid or other properties of materials, such as their viscosity, compliance, and modulus, by rotating, deflecting or oscillating a measuring geometry in a material, either by applying a torque and measuring the resultant velocity or displacement, or by applying a velocity or displacement and measuring the resultant torque. The torque and velocity/displacement are used in conjunction with measuring geometry factors to determine the properties of the material.
As used herein, the term xe2x80x9crheometerxe2x80x9d includes rheometers, viscometers, viscosimeters and similar instruments that are used to measure the properties of fluid or similar materials (see list below).
The term xe2x80x9cmaterial,xe2x80x9d as used herein, includes liquids, oils, dispersions, suspensions, emulsions, adhesives, biological fluids, polymers, gels, pastes, slurries, melts, resins, powders or mixtures thereof. Such materials are also referred to herein as xe2x80x9cfluids.xe2x80x9d More specific examples of materials include asphalt, chocolate, blood, drilling mud, lubricants, oils, greases, photoresists, liquid cements, elastomers, thermoplastics, thermosets and coatings.
A common use for a rheometer is to determine fluid properties of a material. One technique is to apply a torque developed by a drag cup motor in the presence of the material, and measure the resultant velocity or displacement. The torque and velocity/displacement are used in conjunction with measuring geometry factors to determine the properties of the material. It is well known that the torque output of a drag cup motor is dependent on the temperature of the drag cup. For that reason, it is important that the temperature of the drag cup used in the rheometer is known so as to account for an accurate torque measurement used to determine the physical property of the material. If the temperature of the drag cup were not taken into consideration, the accuracy and validity of the measurement of the property of the material would be compromised. Thus it is desirable to measure the temperature of the drag cup to determine its effect on torque.
Despite efforts to maintain a constant and homogenous temperature in the drag cup of a drag cup motor of a rheometer, the actual temperature of the drag cup may fluctuate as it operates thereby affecting the torque output of the motor. Thus, it is desirable to measure the actual temperature of the drag cup as accurately as possible. However, there are difficulties in measuring the actual temperature of the drag cup. For example, one prior art method is to mount a temperature probe in the stator windings of the motor. However, because of a significant air gap between the drag cup and winding, the resulting measurement is likely to be erroneous.
There is, accordingly, a need to develop effective and accurate devices, systems and methods of determining the temperature of a drag cup within a drag cup motor of a rheometer. Furthermore, there is a need to determine the actual temperature of the drag cup in the motor during a time period of a test so as to account for various fluctuations in temperature and their effects on the real-time torque being applied to the material being tested. There is also a need for a flexible yet economic way of measuring the temperature of a drag cup within a rheometer drag cup motor without directly contacting the drag cup or otherwise disrupting its motion within the motor.
The present invention, as described in the exemplary embodiments presented herein, addresses the inefficiencies and inaccuracies that typically occur when estimating the temperature of a drag cup within a drag cup motor of a rheometer. The exemplary embodiments of the present invention provide devices, systems and methods wherein a temperature-sensing component used to calculate the temperature of the drag cup is maintained inside of the motor and in close proximity to motor components without disturbing the motion of the motor.
In its essence, the present invention senses the temperature of a drag cup of a drag cup motor. This temperature, when properly estimated, is then used to adjust/compensate the actual output torque of the motor when testing a given material. The torque is used directly in the determination of the physical property of the given material. Thus, the present invention is used to fine tune and enhance the determination of the physical property of the given material by taking into account that the drag cup within a drag cup motor gets warm during operation, and such heat affects the estimated torque output of the rheometer.
In a preferred embodiment, a drag cup motor is modified to include a coil in communication with a source of current. The coil is arranged to be located in close enough proximity to the drag cup such that the coil can sense the temperature of the drag cup through fluctuations in electrical activity across the coil.
In another exemplary embodiment of the present invention, a device is disclosed for determining the temperature of a drag cup in a drag cup motor of a rheometer. The device includes means for sensing temperature, wherein the means for sensing temperature is in contact with a source of current and is in close enough proximity to the drag cup such that the means for sensing temperature senses the temperature of the drag cup through fluctuations in electrical activity.
In yet another exemplary embodiment of the present invention, a system is disclosed for determining a property of a material. The system includes a rheometer having a drag cup motor, and a coil in communication with a source of current. The drag cup is in close enough proximity to the coil such that the coil senses fluctuations in electrical activity across the coil.
The features and advantages of the present invention will be more fully appreciated upon a reading of the following detailed description in combination with the accompanying drawings.